In a variety of areas of radio wave transmission and reception, it is necessary to control various parameters of a beam of radio waves such as the shape of a phase front or the distribution of amplitude across the beam, etc. It is also necessary to control the shape of a beam (beam forming). One such area is the collecting or launching of radio waves to or from a receiver or transmitter by way of antennas.
It has been a practice that in building radio receivers and transmitters in the cm to sub-mm wavelength range, it is convenient to use strip transmission lines (striplines for short). Waveguides are also in wide use for sending and receiving radio waves to and from high gain antennas, such as paraboloidal reflector antennas, etc. To couple the stripline to a waveguide feed-horn, however, it is necessary to use a transition section. At cm, but especially at mm and sub-mm wavelengths, highly precise machining is necessary to make the transition sections and waveguides. The bandwidth is also relatively narrow.
U.S. Pat. No. 4,500,887, Feb. 19, 1985, to Nester, describes a microstrip notch antenna which overcomes some of these limitations by eliminating waveguide-stripline coupling. In this device, a microstrip line (an asymmetrical single ground plane stripline) is gradually transformed into a flared notch antenna. Some deficiencies of this device are the tendency of microstrip lines to radiate at bends and discontinuities; the capacity of the notch antennas structure to support surface waves; and the difficulty, with a single ground plane, to sandwich a number of planar structures of this type closely together to form an array of antennas.
Various other stripline antennas have been proposed. U.S. Pat. No. 4,335,385, Jun. 15, 1982, Hall, teaches one type of antenna in which an appropriate combination of right-angle corners in stripline produces the desired polarization in radio waves being radiated into free space. U.S. Pat. No. 4,001,834, Jan. 4, 1977, Smith, on the other hand, describes printed wiring antennas and arrays. Each antenna is made of printed wiring on a single card which integrally includes printed transmission feedlines. An array of such cards can be fabricated into a radiant energy lens.